The present invention relates to a process for increasing the capacity of a separation apparatus and an air separation process and apparatus.
Industrial plants frequently treat at least one gaseous mixture by distillation and/or liquefaction and/or adsorption and/or permeation to produce at least one product which may include energy in the form of electricity or steam or a gaseous or liquid product having a composition or state different from that of one of the gaseous mixtures treated.
Generally when the product requirement increases, in a first phase, the capacity of the plant is pushed to the limit by increasing the amount of mixture treated and, if necessary, changing the plant equipment to permit this increase. Once the maximum capacity of the existing plant is not sufficient, a second phase is initiated and a further similar plant is constructed to supply the additional requirements, by itself producing part of the required product.
For example, in many cases, an air separation plant must supply variable amounts of gas and liquid over its lifetime. If the amount of product required increases, in the first phase, the air separation plant can be operated at maximum capacity as disclosed in EP-A-0678317 to increase the amount of air sent to the column.
Additionally different products may be required during the lifetime of the plant. For example, the purity required for a supplied gas may change or a gas not initially needed may subsequently be requested. Thus as described in U.S. Pat. No. 4,869,742 and EP-A-0699884 (S3901), additional trays may be placed within the column of an existing plant or a new column may be added to an existing plant as a retrofit so as to provide a new product. In the examples of
EP-A-0081472 and U.S. Pat. Nos. 4,433,990 and 4,715,874 a plant which produces only oxygen is modified to produce argon also.
GB-A-1416163 and J-A-11325718 disclose modifying an existing plant by increasing the oxygen content of the air fed to the separation unit, using a membrane or a PSA.
Research Disclosure 39361 (January 1997) describes the integration of a mixing column into an existing air separation plant.
U.S. Pat. No. 5,170,630 discloses improving the purity of nitrogen produced by a plant by modifying the condenser and column and adding a phase separation tank and associated piping.
EP-A-0628778 describes an air separation plant in which liquid oxygen from a column of the plant and liquid oxygen from an external source are mixed and vaporized in the heat exchanger of the air separation plant.
In particular, the apparatus and process of the invention allows the capacity of an existing air separation unit to be increased beyond the limits of previously known systems.
It is known for an air separation apparatus to comprise a double column and a further column fed by air. In such cases the further column is commonly a mixing column fed by an oxygen rich liquid at the top of the column as disclosed in U.S. Pat. Nos. 4,022,030, 4,883,517, 5,244,489, 5,291,737 and EP732556.
Nitrogen stripping columns are also known from EP387872, EP532155 and EP542559. In none of these cases is an air stream fed to the column.
It is an object of the present invention to minimize the cost of the second phase by using an additional plant which may or may not directly produce any of the additional product required but which is linked to the existing plant by exchanges of matter and /or energy so that the existing plant can produce the additional quantity of product required as well as new products, in some cases.
Thus the aim of the invention is to increase the amount of a first product of an installation comprising a first existing unit only from A mol. /h before modification to Cmol/h following modification, the production of the first unit being boosted to A+B mol./h, A+B being less than or equal to C and of course greater than A.
The modification consists in incorporating in the installation a second unit and sending energy and/or matter either from the first unit to the second unit or from the second unit to the first unit such that the production of the first unit is boosted to A+B.
In certain cases, where A+B is smaller than C, the difference Bxe2x80x2 mol./h may be produced directly by the second unit and mixed with A+B from the first unit to produce C om the whole installation.
The pressure of the first product in amount A and amount C may vary by up to 5 bars.
The temperature of the first product in amount A and amount C may vary by up to 25xc2x0 C., or preferably 5xc2x0 C.
It will generally be the case that the total amount of feed in mol./h sent to the existing first unit before modification will be less than the total amount of feed sent to the first unit (or to the first and second units if feed is sent to both).
According to a first embodiment of the invention, there is provided a process for increasing the amount of at least one product produced by a first unit for treating at least one fluid mixture by at least one of the group of processes comprising pressurization, expansion, distillation, mixing in a mixing column, liquefaction, adsorption and permeation wherein at least one fluid mixture is sent to the first unit and at least one product is removed from the first unit, said product having a different composition from said at least one fluid mixture and optionally a different state and/or a different pressure from said at least one fluid mixture, wherein the first unit alone before integrating a second unit to the first unit produces an amount A moles/h of a first product and said amount of first product withdrawn from the first unit and optionally from the second unit is increased to C moles/h, C being greater than A, and the amount C comprising at least one fluid stream withdrawn from the first unit and optionally from the second unit, by integrating the second unit with the first unit, said integration comprising sending energy and/or at least one fluid from the first unit to a second unit and/or from the second unit to the first unit, wherein said second unit treats at least one fluid mixture by at least one of the group of processes comprising pressurization, expansion, warming, cooling, distillation, mixing in a mixing column, liquefaction, adsorption and permeation such that the first unit produces an amount of first product A+B moles/h.
The first unit comprises means for carrying out at least one of the group of processes comprising pressurization, expansion, distillation, mixing in a mixing column, liquefaction, adsorption and permeation. It may also include other means such as pretreatment means for cooling and/or purifying and/or compressing, storage means or insulation means, for example a cold box.
The second unit comprises means for carrying out at least one of the group of processes comprising pressurization, expansion, warming, cooling, distillation, mixing in a mixing column, liquefaction, adsorption and permeation. It may also include other means such as pretreatment means for cooling and/or purifying and/or compressing, storage means or insulation means, for example a cold box.
The amount of first product may be increased such that A+B is less than or equal to C.
Where A+B is less than C, the difference between C and A+B is an amount of product Bxe2x80x2 moles/h produced by the second unit.
The compositions of the first product before and after integration need not be strictly identical: for example the percentage of principal component in the first product in amount A and amount C may differ by up to 5 mol. %, up to 1 mol. % or up to 0.2 mol. %.
Similarly the composition of the first product produced by the first and second units, before or after integration need not be strictly identical: for example the percentage of principal component in the first product in amount A and amount Bxe2x80x2 may differ by up to 10 mol. % or up to 5 mol. % or up to 2 mol. %
In some cases, the second unit treats a mixture having substantially the same composition as the mixture treated by the first unit.
In some cases the second unit produces a second product having a percentage of principal component differing by 1 to 50% from the percentage of the first product of the first unit forming part of amount A+B or having a different principal component and/or state and/or pressure from the first product of the first unit forming part of amount A+B.(FIG. 2)
Generally, the amount of feed in moles sent to the first unit for the production of amount A only is less than the amount of feed in moles sent to the first unit for the production of amount C.
Where the second unit produces part of increased amount C, the amount of feed in moles sent to the first unit for the production of amount A only may be less than the amount of feed in moles sent to the first and second units for the production of amount C.
In general, the proportional increase in amount of feed in moles sent to the first unit for the production of amount C following the addition of the second unit as compared with the production of amount of feed in moles sent to the first unit for the production of amount A prior to the addition of the second unit may be less than, equal to or greater than the proportional increase between amount C and amount A.
The fluid mixture treated by the first and second units may for example be substantially air and the first product may contain at least 70 mol. % oxygen or at least 90 mol. % nitrogen or at least 90 mol. % argon.
In other cases, the fluid mixture treated may be a mixture comprising at least 1 mol. % nitrogen and/or at least 1 mol. % hydrogen and/or at least 1 mol. % carbon monoxide and/or at least 1 mol. % methane and the first product may contain at least 90 mol. % nitrogen or at least 90 mol. % hydrogen or at least 90 mol. % carbon monoxide or at least 90 mol. % methane.
In some cases the second unit does not treat the same mixture as the first unit.
In preferred embodiments, the first and/or second units may treat the mixture or mixtures by cryogenic distillation and/or liquefaction.
The first product may be removed from the first unit in gaseous form and/or at least one liquid may be removed from a column of the first unit and is vaporized to form the first product and then withdrawn from the first unit in gaseous form to form all or part of the rest of the gaseous first product.
Preferably the second unit modifies the composition of at least one fluid mixture fed thereto, for example by separating it (or mixing them) to form at least two fluids, each of which is enriched in one of the components of the fluid mixture.
Optionally the second unit produces at least one product having a different composition or pressure to the first product produced by the first unit and/or at least one product of the second unit is not mixed with the first product of the first unit which is to be produced in increased quantities.
In preferred embodiments, following integration of the second unit at least one fluid from the second unit is sent to the first unit as a feed stream to be separated and/or treated within the first unit.
Preferably at least one fluid sent from the second unit to the first unit is richer in the principal component of the first product than the fluid mixture sent to the first and/or second unit or than the first product.
In this case, the fluid sent from the second unit to the first unit may be richer in the principal component of the first product than the fluid mixture sent to the first and/or second unit but less rich in the principal component of the first product than the first product.
Preferably, following integration of the second unit, at least one fluid from the first unit is sent to the second unit as a feed stream to be separated, mixed and/or treated (e.g. heated or cooled) within the second unit.
In some cases the fluid sent from to the first unit to the second unit is less rich in the principal component of the first product than the fluid mixture sent to the first and/or second unit or than the first product and in particular cases the fluid from the second unit is richer in the principal component of the first product than the fluid mixture sent to the first or second unit but less rich in the principal component of the first product than the first product.
Preferably, following integration of the second unit, at least one fluid is removed from the first unit which is less rich in the principal component of the first product than the at least one fluid sent from the second unit to the first unit.
The at least one fluid sent from the second unit to the first unit contains at least 10 mol. % less, preferably at least 25 mol. % less or even at least 50 mol. % less, of the principal component of the first product than the at least one product removed from the first unit.
In one embodiment, following integration of the second unit a fluid from the second unit is sent to the first unit and is used to provide additional reboil in the first unit.
Alternatively or additionally following integration of the second unit, a fluid from the second unit is sent to the first unit and is used to provide additional condensation in the first unit.
The second unit need not produce a product.
The second unit may produce energy and the first unit need not produce energy.
Preferably the first unit produces part A+B of the at least one first product stream and the second unit produces the rest Bxe2x80x2 of the at least one first product stream, the parts of the at least one first product stream having a common principal component and the pressures of the part of the first product streams having a common principal component differ by at least 0.5 bar and/or 20% of the pressure of the higher pressure stream.
Additionally the first unit produces part A+B of the at least one first product stream and the second unit produces the rest of the at least one first product stream, the part s of the at least one first product stream having a common principal component and the parts of the first product streams having a common principal component are in different physical states.
The first unit may produce at least one first product stream and the second unit may produce at least one second product stream and the second product streams do not have the same principal component.
Preferably the amount of fluid sent from the first unit to the second unit in moles/h is substantially equal to the amount of fluid sent from the second unit to the first unit in moles/h or differs from that amount by no more than 50%, preferably by no more than 30% or even 10%.
Preferably where fluids are transferred from the second to the first unit and vice versa, either both or all the fluids are liquids or either both or all the fluids are gases.
Preferably the amount of fluid sent from the first unit to the second unit in m3/h is substantially equal to the amount of fluid sent from the second unit to the first unit in m3/h or differs from that amount by no more than 50%, preferably by no more than 30% or even 10%.
According to a preferred embodiment, the first unit is an air separation unit producing at least one fluid enriched in a component, wherein air is sent to the first unit and at least one fluid enriched in a component of air is removed from the first unit as a first product, an amount A moles/h of the first product being removed prior to the integration of a second unit and by sending energy or fluid from the first unit to the second unit and/or from the second unit to the first unit, the amount of first product which is produced by the first unit increases to A+B moles/h, wherein said second unit treats at least one gaseous mixture containing oxygen and nitrogen by at least one of the group of processes comprising distillation, mixing in a mixing column, liquefaction, adsorption and permeation such that the amount of fluid enriched in a component of air produced by the first unit and optionally by the second unit as said first product is increased to C moles/h, where C is greater than A. (FIGS. 2,4,5 and 6)
In this case, optionally, the first unit produces at least one first product stream and the second unit produces at least one second product stream and at least one second product streams has the same principal component as the at least one first product stream but the percentage of principal component contained in the first and second product streams having a common principal component differs by at least 5 mol.-% where the common principal component is oxygen or argon or the amount of minor components differs by at most a factor of 10 where the common principal component is nitrogen.
Preferably the percentage of principal component contained in the first and second product streams having a common principal component differs by at least 10 mol.-% or at least 20 mol.-% where the common principal component is oxygen or argon.
Preferably, the amounts of first product A and C or A and A+B have the same principal component and the amount of principal component differs between amounts A and C (or A and A+B) by at least 0.2 mol. %, preferably at least 1 mol. % or the amount of minor components differs by a factor of at most 1.2, preferably 2 where the principal component is oxygen or argon.
Attentively the amounts of first product A and C or A and A+B have the same principal component which is nitrogen and the amount of minor components in moles in A and C (or A and A+B) differs by at least a multiple of 10.
Preferably the amounts of first product A and C or A and A+B have the same principal component and the amount of principal component in product C (or A+B) is less than, greater than or equal to the amount of principal component in A.
In some cases, the fluid or fluids sent from the second unit to the first unit is(are) removed from the second unit at a subambient temperature and is (are) supplied to the first unit at a subambient temperature and/or wherein the fluid or fluids sent from the first unit to the second unit is (are) removed from the first unit at a subambient temperature and is (are) supplied to the second unit at a subambient temperature.
Alternatively the fluid or fluids sent from the second unit to the first unit is(are) removed from the second unit at a cryogenic temperature and is (are) supplied to the first unit at a cryogenic temperature and/or wherein the fluid or fluids sent from the first unit to the second unit is (are) removed from the first unit at a cryogenic temperature and is (are) supplied to the second unit at a cryogenic temperature.
The fluid or fluids sent from the second unit to the first unit may be removed from the second unit at any temperature and may be supplied to the first unit at any temperature and/or the fluid or fluids sent from the first unit to the second unit may be removed from the first unit at any temperature and may be supplied to the second unit at any temperature.
Preferably in the process for increasing the amount of fluid enriched in a component of air produced by a first existing air separation unit for treating air by distillation from A mol./h to produce C mol./h wherein air is sent to the first unit and at least one fluid enriched in oxygen is removed from the first unit as a product and by sending the fluid enriched in oxygen from a second unit to the first unit the amount of first product produced by the second unit being increased to A+B mol./h, wherein said second unit treats a gaseous mixture by at least one of the group of processes comprising pressurization, expansion, warming, cooling, distillation, mixing in a mixing column, liquefaction, adsorption and permeation such that the amount of fluid enriched in oxygen produced by the first unit is increased.
The second unit may be a single column cryogenic distillation unit fed by cooled and purified air and the oxygen enriched fluid is derived from the bottom of the column and contains between 25 and 45 mol. % oxygen.
Alternatively the first unit comprises at least a high pressure column and a low pressure column and air is fed at least to the high pressure column and the oxygen enriched fluid from the second unit is fed to the first unit, wherein it is separated, mixed and/or treated.
In this case, the sole product of the second unit may be a nitrogen enriched fluid.
Preferably a fluid enriched in nitrogen is sent from the first unit to a heat exchanger of the second unit and is warmed therein.
Preferably liquid enriched in nitrogen (140) is sent from the second unit (125, 130, 133) to the first unit to serve as reflux.
Preferably oxygen enriched liquid from the first unit is vaporized in the second unit, specifically in the heat exchanger of the second unit.
In one embodiment the process comprises sending compressed and cooled air to at least one first distillation column of a first air separation unit comprising at least one column and removing oxygen enriched fluid and nitrogen enriched fluid from the first unit and sending compressed and cooled air to a second unit comprising a single distillation column having a top condenser, condensing nitrogen enriched gas at the top of the single column of the second unit in the condenser, removing nitrogen enriched fluid from the second unit, optionally following an expansion step of at least part thereof, removing oxygen enriched liquid from the column of the second unit and sending it to the condenser to form vaporized oxygen enriched liquid, optionally following a distillation step and sending vaporized and/or unvaporized oxygen enriched liquid to a column of the first air separation unit and withdrawing oxygen enriched fluid at least from the first air separation unit as a product.
The air separation unit may comprise at least two distillation columns and said first distillation column is the column operating at the higher or highest pressure and the oxygen enriched product is removed from a column operating at a lower or the same pressure.
Optional features include:
sending said vaporized and/or unvaporized oxygen enriched liquid from the second unit to the first unit to be distilled and/or treated.
sending said vaporized and/or unvaporized oxygen enriched liquid to another column of the air separation unit.
sending said unvaporized oxygen enriched liquid to at least the first distillation column of the first unit.
sending said unvaporized oxygen enriched liquid to another column of the air separation unit.
sending said vaporized oxygen enriched liquid to the condenser of an argon column, to a low pressure column or to a mixing column.
the air sent to the second unit is at a higher pressure than, a lower pressure than or an equal pressure to any air stream sent to the first unit.
removing product nitrogen from the second unit.
expanding at least part of the nitrogen enriched gas removed from the second column in a turbine.
Another process for increasing the capacity of a first air separation unit in which a first air stream is separated by cryogenic distillation in a first air separation unit from which an oxygen enriched fluid is removed comprising adding a second unit to the existing first unit, sending a second air stream air to the bottom of a column of the second unit sending a nitrogen enriched liquid stream from the first air separation unit to the top of the column of the second unit, removing a gaseous nitrogen stream from the top of the column of the second unit, sending an oxygen enriched liquid stream from the column of the second unit to the first unit and removing an increased amount of the oxygen enriched fluid from the first unit.
Optional features of this process include:
said column of the second unit is a single column having no bottom reboiler and no top condenser.
sending air from a second compressor to the second unit and optionally to the first unit.
pressurizing or expanding the nitrogen enriched liquid from the first unit, and sending it to the top of the column of the second unit.
the column of the second unit operates at between 1.2 and 25 bar, preferably above 4.5 bar, still more preferably above 9 bar.
the pressure of the higher or highest pressure column of the first unit is between 4 and 25 bar.
the oxygen enriched liquid at the bottom of the column of the second unit contains between 25 and 50 mol. % oxygen, preferably between 30% and 40% oxygen.
the first air separation unit comprises at least one double column comprising a high pressure column and a low pressure column and the nitrogen enriched liquid comes from the high pressure column and/or the low pressure column.
sending the fluid from the bottom of the column of the second unit to the bottom of the high pressure column or to the low pressure column.
removing a first product stream containing at least 80 mol. % oxygen from the low pressure column of the first unit.
the first air separation unit is a triple column comprising a high pressure column, an intermediate pressure column and a low pressure column and the nitrogen enriched liquid is sent from the high pressure column or the intermediate pressure column to the second unit.
sending the fluid from the bottom of the column of the second unit to the high pressure column or the intermediate pressure column or to the low pressure column.
removing a first product stream containing at least 80% oxygen from the low pressure column of the first unit.
In another embodiment, there is provided a process wherein an existing air separation unit produces an amount A of an oxygen enriched product stream as first product, a second unit comprising a mixing column is integrated with the first unit and, subsequently, oxygen enriched liquid is sent from the first unit to the top of the mixing column, a gas more volatile than the oxygen enriched liquid is sent to the bottom of the mixing column and a fluid enriched in oxygen is sent from the mixing column to the first unit.(FIGS. 4 and 5)
The mixing column operates at a cryogenic temperature.
Optionally:
the fluid enriched in oxygen sent from the mixing column to the first unit is a heating stream for a vaporizer-condenser of a column of the first unit.
the fluid enriched in oxygen is sent to a column of the first unit, preferably to a low pressure column of a double column, as a feed stream preferably following at least partial condensation in a vaporizer-condenser of the low pressure column.
the gas more volatile than the oxygen enriched liquid is air or vaporized oxygen enriched liquid from the bottom of the high pressure column of the double column which constitutes the first unit.
According to another embodiment, there is provided an air separation apparatus having a first unit comprising at least a high pressure column and a low pressure column and possibly an intermediate pressure column which are thermally linked, a second unit comprising means for cryogenic distillation of air, means for removing a stream containing more than 20 mol % oxygen from a column of the second unit, means for sending the stream containing more than 20 mol. % oxygen to the high and/or intermediate and/or low pressure column, means for sending cooled and purified air at least to the high pressure column and to the second unit and means for removing an oxygen enriched product stream fromat least one unit.
Optional features of this embodiment include:
a second unit comprising a single column having a top condenser, means for feeding cooled and purified air to the single column, means for sending a bottom liquid from the bottom of the column to the top condenser and wherein the means for producing a stream containing more than 20 mol. % oxygen links the top condenser and/or the single column with a column of the first unit.
means for removing at least a nitrogen enriched fluid from the single column.
conduit means links the top condenser of the second unit so as to remove a liquid and a gas containing at least 20 mol. % oxygen therefrom and is connected to the high pressure column and/ the low pressure column of the first unit.
means for removing the oxygen enriched stream from the low pressure column of the first unit in liquid form and vaporizing the stream so to form the gaseous product stream.
means for sending the stream containing more than 20 mol. % oxygen to the high and/or intermediate and/or or low pressure column of the first unit, said means being connected downstream of a heat exchanger of the first unit wherein air to be distilled in the high pressure column is cooled to a temperature suitable for distillation.
means for sending nitrogen enriched fluid from the first unit to the second unit and/or from the second unit to the first unit.
means for sending at least one fluid from the first unit to the second unit and means for expanding the fluid from the first unit within the second unit.
means for sending at least one liquid from the first unit to the second unit and means for vaporizing the fluid from the first unit within the second unit, preferably in a heat exchange line of the second unit.
In particular the process may be an integrated gasification combined cycle process in which oxygen from the air separation unit is sent to gasify a carbon containing substance thereby producing fuel for the combustor.
The term xe2x80x9cfluid mixturexe2x80x9d covers gaseous or liquid streams containing at least two components which have a different chemical composition. The fluid may alternatively contain both gaseous and liquid phases.
The term xe2x80x9csubambient temperaturexe2x80x9d means a temperature below 10xc2x0 C.
The term xe2x80x9ccryogenic temperaturexe2x80x9d means a temperature below xe2x88x92100xc2x0 C.
The term xe2x80x9cproductxe2x80x9d means a gas or liquid which is removed from one of the units, does not return to either of the units and is not sent directly to the atmosphere.
The term xe2x80x9cClaude turbinexe2x80x9d means an air turbine whose exit is connected to a distillation column of the system other than the column operating at the lowest or lower pressure.
The term xe2x80x9cfluidxe2x80x9d means a gas or a liquid, a gas and a liquid or a dual phase gaseous-liquid mixture.